Field of Endeavor
The present application relates to sensors and more particularly to a UV laser based stand-off acoustic sensor.
State of Technology
This section provides background information related to the present disclosure which is not necessarily prior art.
U.S. Pat. No. 6,731,570 for sound detection provides the state of technology information in the portions of the patent that are reproduced below.
“This invention relates to improvements in or relating to sound detection, in particular to a remote sound detector and a method of remote sound detection. Acoustic signals are frequently used for detecting and locating remote objects such as guns and vehicles on a battlefield. Sensitive directional acoustic receivers arc able to determine the direction of acoustic signals emanating from powerful remote sources with considerable accuracy. This enables the determination of the position of the source from which the acoustic signal is emanating, provided that there are no intervening obstacles to attenuate or diffract the acoustic signal. There are several known laser techniques used for measuring the velocity of air or airflow from a remote position, for example the measurement of air velocity and airflow profile in a wind tunnel using a laser beam passed into the airflow through a window. A typical technique employs a laser to produce two beams intersecting at an angle at a point within the airflow, producing interference fringes in the region where the beams overlap. Thus particles propelled by the airflow through the fringes produce scattered light which is modulated periodically by the passage of the particles through the fringes. The frequency of modulation, detected by an optical receiver, provides a measurement of the particle velocity and hence the airflow velocity. This technique is difficult to employ effectively at a range of more than a few meters from the laser source. Therefore a different technique is required to make measurements at longer ranges.”
U.S. Pat. No. 8,599,649 for a laser-based method of detecting underwater sound through an ice layer provides the state of technology information in the portions of the patent that are reproduced below.
“The purpose of the invention is to detect underwater acoustic sound impinging on an ice object that is partially submerged in water by using a laser Doppler vibrometer sensor to measure the surface velocity and therefore an acoustic pressure signal at the ice surface being probed. As noted, a surface with a poor reflective quality due to angled or snow-covered ice surfaces and motion of the ice will degrade sensor performance by increasing the signal dropout rate. A solution is to monitor the ice surface using an illuminating source and record the reflected light using a camera to identify the trajectory to areas of direct reflection back to the laser source and to actively steer the sensing laser along that trajectory onto a glint retro-reflection surface using a glint tracking device. The result is that the laser is steered onto a position where the LDV will receive a direct reflection from the ice surface.”
U.S. Pat. No. 8,228,760 for an airborne laser-acoustic mine detection system provides the state of technology information in the portions of the patent that are reproduced below.
“The present invention includes a system and method for using acoustical pulses generated from an airborne laser source to identify and locate targets under water. An array of acoustic sensors, such as passive sonobuoys at the ocean surface, is deployed by aircraft so that three or more acoustic sensors are within a predefined range from objects to be detected. The position of the acoustic sensors is known at the time of deployment or can be determined after deployment, for example by including a global positioning system (GPS) receiver in each sensor or by determining acoustic travel times from multiple known laser-acoustic source locations to each sensor. Each area surrounded by three or more acoustic sensors comprises a search cell, within which sonar scattering data can be used to locate objects. The maximum size of the search cells can be determined by parameters such as the acoustic source power spectrum, a target object's acoustic reflectivity, and the corresponding acoustic attenuation distance.”